We plan to investigate the occurrence of trans isomers of fatty acids in human aorta and to relate its level to the severity of atheromata. We further plan to investigate the influence of trans isomers upon the metabolism of fatty acids and lipids. Trans fatty acids will be analyzed by GLC in diagnostic tissue from endarectomies where arteriograms have been made to establish the degree of atheroma. We will synthesize all isomers of trans octadecenoic acid and compare relative rates of reaction of these isomers in several fatty acid metabolism enzyme systems, including chain elongation, chain shortening, desaturation, and acyl incorporation of trans acids into PL and TG using liver microsomes from normal and essential fatty acid-deficient rats. Mixed randomized triglycerides containing some of these fatty acid isomers will be hydrolyzed with pancreatic lipase to determine the degree of discrimination for the double bond position and trans isomers. The pure isomers will also be subjected to hydrolysis by a cholesterol esterase isolated from swine artery in this laboratory. Studies will be made with liver microsomes from rats fed corn oil or hydrogenated fat containing 50% trans acids, to determine their specificity in these enzyme reactions.